Ocean thermal energy conversion(OTEC)is a hot research topic in the field of ocean renewable energy. The developments of OTEC resource assessment, resource distribution, and cycle mode as well as the OTEC demonstration project were reviewed and analyzed. Then, the key technologies of OTEC from the stability of power generation platform, the comprehensive utilization of cold water, the efficiency improving, the multi ocean renewable energy complementary and the environment effect of OTEC plant have been discussed. Although the development of OTEC is feasible and necessary, there are still many challenges and difficulties to solve.